1. Field of the Invention
This invention relates to a method and apparatus for accurately determining equipment depth in a wall taking into consideration stretch of the wire line and errors in measurement of split block separation when a split block is used.
Measurement of the wire line stretch also provides an accurate way to determine the hookload on the traveling block of a drilling rig.
2. Prior Art
The accurate measurement of equipment depth in a well is of major importance.
Numerous ways have been developed for measuring equipment depth by measuring movement of the wire line. This measurement must be corrected to take into account the line stretch. Usually the line stretch is determined by measuring the hookload and deriving the line stretch from hookload and the modulus of elongation for the wire line.
However, it is difficult to measure the absolute value of the hookload. Hookload measurements are hard to verify and are usually assumed to be inaccurate. Calibration for a hookload measurement instrument cannot be achieved with accuracy.
Hence, corrections for line stretch based upon the measurement of hookload are inaccurate and that leads to inaccuracy in the measurement of equipment depth in a well.